@startuml
abstract class Shape {
    {abstract} + getArea(): double
}

class Circle {
    - radius: double
    + getArea(): double
}

class Rectangle {
    - width: double
    - height: double
    + getArea(): double
}

class Triangle {
    - base: double
    - height: double
    + getArea(): double
}

class ShapeUtil {
    + printArea(Shape): void
}

Shape <|-- Circle
Shape <|-- Rectangle
Shape <|-- Triangle
ShapeUtil ..> Shape
@enduml